evil redirect fix (WIP)

@kmcphillips @alexcoco 

Guys, following the fix/issue https://github.com/Shopify/shopify-app-store/pull/361 we need to address the same issue present in our applications and in our gem.

This code works because I tested on Product Reviews but I guess that at this point we need to test the templates in the gem. As I have no tests, and I have no idea how add them to the project, this PR is still a WIP. 

I might try something tomorrow on adding tests to this. Ideas/links/commit are welcome!

We should address this issue in ALL our applications.

I also think we should push the tests as generators as well (but this is another issue) to the hosting application.